How large is this? I am looking for something large for demonstrations.

Item # A76-9 is 2.36" x 15.75" x 15.75". You may be interested in item # A76 - Lumbar Vertebrae Teaching Model. It includes 2 lumbar vertebrae with spinal nerves, dura mater of spinal cord and 2 replaceable dorso-lateral prolapsed discs between the 4th and 5th lumbar vertebrae and is on a removable stand.